This invention relates to diesel engine emission controls and, more specifically, to methods of optimizing fuel injection timing for NOx emission control in a diesel engine.
The Environmental Protection Agency (EPA) requires diesel locomotives to comply with emission regulations over a wide range of ambient temperatures and pressures. More specifically, locomotive emissions are regulated in ambient temperatures between 45xc2x0 F. and 105xc2x0 F. and ambient pressures between 26-31 inches of mercury.
In order to meet emission regulations set forth by the EPA, engines used in diesel locomotives are set to operate with fixed fuel injection timing, which is retarded adequately to limit the formation of nitrogen oxides (NOx) for compliance with EPA emission regulations at all applicable operating temperatures and pressures. However, a drawback to retarded injection timing is that it can increase smoke, particulate emissions and fuel consumption. In addition, the amount of injection retard required to reduce NOx levels under one set of operating conditions may not be required under other conditions.
The present invention provides an emission control system for setting optimal fuel injection timing to meet EPA emission regulations and maximize engine fuel efficiency over a wide range of operating temperatures and pressures. In an exemplary embodiment, the emission control system determines optimal injection timing by determining air density and air flow within an engine and comparing the air density and air flow values to a fuel injection timing map calibrated to comply with emission regulations.
The emission control system includes a control module connected to an air pressure sensor, an air temperature sensor, an engine boost pressure sensor, and an engine fuel injection timing module which is connected to at least one fuel injector or injection pump in a fuel injection system.
The air pressure sensor determines the inlet air pressure and relays the information to the control module. The air temperature sensor determines the inlet air temperature and relays the information to the control module. The boost pressure sensor detects engine boost pressure and relays the boost pressure information to the control module. The information relayed to the control module is used to calculate inlet or ambient air density and the air flow rate through the engine. The control module uses the air density and air flow rate, information to determine an optimal fuel injection timing, or most advanced timing possible, while still complying with emission regulations. The fuel injection timing information is then relayed to the fuel injection timing module to alter the timing of the fuel injector(s). The emission controller operates to recalculate the optimal fuel injection timing and alter injector timing accordingly to operate the engine as efficiently as possible within the emission limits.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.